Source of negatively charged particles having positively charged particle retaining means



March 26, 1968 TIVELY T. CONSOLI ETAL SOURCE OF NEGATIVELY CHARGEDPARTICLES HAVING POSI CHARGED PARTICLE RETAINING MEANS Filed Sept. 30,1965 United States Patent SOURCE OF NEGATIVELYCHARGED PARTICLES HAVINGPOSITIVELY CHARGED PARTICLE RETAINING MEANS Terenzio Consoli, LaCelle-Saint-Cloud, and Richard Geller, Antony, France, assignors toCommissariat a lEnergie Atomique, Paris, France Filed Sept. 30, 1965,Ser. No. 491,700 Claims priority, application France, Oct. 14, 1964,

91,422 2 Claims. (Cl. 315111) ABSTRACT OF THE DISCLOSURE The presentinvention relates to source of negatively charged particles, inparticular an electron source adapted to generate a very high-energyelectron beam.

The known electron sources, in particular those-of the thermoionic type,usually comprise a first electrode, or'

cathode, which is raised to a certain temperature and emits electrons,said cathode being in register with a positive electrode. The electricfield thus established between these two electrodes permits toaccelerate, and conting ently to focus, the electrons emitted by saidcathode.

The intensity of the electron beam thus obtained is limited by theemitting power of the cathode and by a space charge which tends to repeltowards the latter a large proportion of the electrons emitted. Thelimitation due to the space charge, localized in the vicinity of thecathode and known under the name of Child-Langmuir effeet, ispreponderant and due in particular to the fact that since the electronsleave the cathode with initial velocities which are both very low andrandomly orientated, the electronic density is very high in the vicinityof said cathode, where the action of the electric field is very small.

Moreover, the known electron guns, which can be applied in particular tothe devices for welding by electron bombardment, contain an electronsource which generates a beam the intensity of which is in generallargely limited by the space charge.

The present invention, which is free of the above drawbacks, relates toa source of negatively charged particles, and in particular an electronsource adapted to generate a very high-energy electron beam, said sourcecomprising means for generating an accelerated jet of positively chargedparticles and of negatively charged particles which is altogetherelectrically neutral and possessed of a very high energy, at least twoelectrically conductive parallel plates at right angles to thelongitudinal axis of said jet, said plates being provided with openingsco-axial to said jet and the areas of which are of the order of that ofthe cross-section of said jet, and a source of direct current adapted toestablish an electric field between said plates and so mounted that itsnegative terminal is connected to that of said plates which is the moreupstream of said jet, whereby when said jet has passed through saidopening of said upstream plate, the positively charged particles of saidjet, due to said electric field, are slowed down and then, sent backtowards said upstream plate by ICC which they arecaptured, whereas thenegatively charged particles proceed on their way and pass through theopen ing of the other plate after having been accelerated by saidelectric field.

According to a specific form of embodiment, said jet of particles isconstituted by a plasma emitted by an electro-magnetic accelerator.

Said source of negatively charged particles can comprise means locatedbetween said means for generating an accelerated jet and said twoplates, and adapted to generate a magnetic field which is parallel tothe longitudinal axis of said jet and the intensity of which increasesin the direction of flow of said jet, said magnetic field permitting tofocus the negative particles in the vicinity of the axis of said jet. 7

The features of the present invention will be disclosed hereafterreference being had to the accompanying drawing which diagrammaticallyrepresents a source according to the invention, shown in section along aplane passing through the axis of the jet of particles, said jet beingassumed as constituted by an accelerated plasma emitted by anelectro-magnetic accelerator.

In the figure, an accelerator of ionised gas or plasma isdiagrammatically shown at 1. This accelerator emits a jet of plasma 2possessed of a very high energy, which is altogether electricallyneutral and composed of positive ions and of electrons, the velocity ofthe positive ions being substantially equal to the component of theelectron velocity along the axis XX of the jet.

The electrons of jet 2 follow helical paths whereas the ions, driven bythe electronic spacecharge, move in the direction of axis XX. The energyof the flux of particles forming jet 2 is proportional to theelectro-magnetic power of accelerator 1, which is for instance of 300w., the electron energy being then of the order of 10 ev. and the totalnumber of particles emitted per second of the order of 10 A coil 3co-axial to the plasma jet 2 generates a static magnetic field which isparallel to the longitudinal axis of said jet, and the intensity ofwhich increases in the direction of flow of said jet.

Two circular openings 4 and 5 co-axial to the plasma jet 2 and the areasof Whichare of the order of that of the cross-section of said jet, areprovided in two parallel conductive plates, 6 and 7 respectively,connected to the terminals of a direct current source 8, plate 6 locatedbetween coil 3 and plate 7 being connected to the negative terminal ofsaid source 8.

Any electron contained in plasma jet 2 undergoes, when passing throughcoil 3, the action of the magnetic field generated by said coil, and ifthis magnetic field, which is co-axial to jet 2, is graduallyincreasing, it causes a decrease of the radius of the helical pathfollowed by said electron. Therefore the major portion of the electronswhich pass through said coil are concentrated in the vicinity of theaxis of jet 2, thus forming a beam which converges towards opening 4 andpasses through said opening. As stated above, the electrons move in thedirection of axis XX and therefore in the direction of the magneticfield. Accordingly, the magnetic field exerts no action upon theelectrons and they are not deviated and all of the electrons passthrough opening 4.

The ions of the jet are not deflected by the magnetic field, since theirvelocity is parallel to said field; therefore they also pass throughopening 4 and they are then submitted to the decelerating electric fieldestablished between plates 6 and 7. This electric field, the lines offorce of which are substantially parallel and directed from plate 7 toplate 6, slows down the ions and then sends them back towards plate 6 bywhich they are captured. Plate 6 thus permits to set apart, within beam2, the ions from the electrons, and only the latter are able to passthrough opening 5.

One can then obtain, beyond plate 7, an electron beam 9 the electrons ofwhich have their energy still increased by the acceleration which theyundergo between plates 6 and 7. The ions captured by plate 6 are drivenby conduction to source 8.

Since the energy of the electrons contained in beam 2 is already veryhigh before they pass through opening 4, the space charge created in thevicinity of said opening has no substantial action on electron beam 9and the drawback arising from the child-Langmuir effect is thereforeavoided.

Accelerator 1 and plates 6 and 7 are located in a tight enclosure (notshown), inside which the air pressure is maintained at about atmosphere.

The intensity of the electron beam delivered by the source according tothe present invention is, for instance, of the order of 1 A./cm. thediameter of openings 4 and 5 being 1 cm. and the voltage delivered bysource 8 being of 500 v.

Such a source associated to an accelerating and focusing device of aknown type, is capable of generating a very strong electronic beampermitting to carry out welding by electronic bombardment, and it canadvantageously replace the thermoionic sources usually associated to theelectron guns provided for this purpose.

What is claimed is:

1. A device for sorting out the electrons and positive ions from anaccelerated jet of positively charged particles and negatively chargedparticles which is altogether electrically neutral and possessed of aveiy high energy for retaining positive ions and emitting electronsincluding a source for said jet, at least two electrically conductiveparallel plates at right angles to the longitudinal axis of said jet,said plates being provided with openings co-axial to said jet and theareas of which are of the order of that of the cross-section of saidjet, a source of direct current adapted to'establish an electric fieldbetween said plates and so mounted that its negative terminal isconnected to that of said plates which is the more upstream of said jet,and a coil located entirely between said means for generating anaccelerated jet and said two plates and generating a magnetic fieldwhich is parallel to the longitudinal axis of said jet and the intensityof said magnetic field increases continuously in the direction of fiowof said jet, whereby said negatively-charged particles are caused toconverge towards said longitudinal axis and, once said jet has passedthrough said opening of said upstream plate, the positively-chargedparticles of said jet, due to said electric field, are slowed down andthen sent back towards said upstream plate by which they are captured,whereas the negatively-charged particles proceed on their way and passthrough the opening of the other plate after having been accelerated bysaid electric field.

2. A source of electrons adapted to generate a very high energy electronbeam, said source comprising an electromagnetic accelerator adapted toemit a jet of plasma possessed of a very high energy, at least twoelectrically conductive parallel plates at right angles to thelongitudinal axis of said jet, said plates being provided with openingsco-axial to said jet and the areas of which are of the order of that ofthe cross-section of said jet, a source of direct current adapted toestablish an electric field between said plates and so mounted that itsnegative terminal is connected to that of said plates which is the moreupstream of said jet, and a coil located entirely between said means forgenerating an accelerated jet and said two plates and generating amagnetic field which is parallel to the longitudinal axis of said jetand the intensity of said magnetic field increases continuously in thedirection of flow of said jet, whereby the electrons of said plasma arecaused to converge towards said longitudinal axis and once said jet haspassed through said opening of said upstream plate, the positive ions ofsaid plasma, due to said electric-field, are slowed down and then sentback towards said upstream plate by which they are captured, whereas theelectrons of said plasma proceed on their way and pass through theopening of the other plate after having been accelerated by saidelectric field.

References Cited UNITED STATES PATENTS 2,489,082 11/1949 De Forest 3l385X 2,975,279 3/1961 Craig 25041.9 3,082,326 3/1963 Arnold 3l3-6l3,275,867 9/1966 Tsuchimoto 3 l363 3,287,582 11/1966 Baldwin 313-63JAMES W. LAWRENCE, Primary Examiner.

STANLEY D. SCHLOSSER, Examiner.

S. A. SCHNEEBERGER, Assistant Examiner.

